Frequently Asked Questions about Motor Vibration Failure

The vibration of the motor will shorten the winding insulation and bearing life, and affect the normal lubrication of the sliding bearing. The vibration force promotes the expansion of the insulation gap, causing external dust and moisture to invade it, resulting in a decrease in insulation resistance and an increase in leakage current, and even an insulation breakdown Wait for the accident.

Ten reasons for motor vibration

1) It is caused by the imbalance of the rotor, coupler, coupling, and transmission wheel (brake wheel).

2) The iron core support is loose, the oblique key, the pin is invalid and loose, and the rotor is not tightly bound, which will cause the rotating part to be unbalanced.

3) The shaft system of the linkage part is misaligned, the center line does not coincide, and the centering is incorrect. This kind of failure is mainly caused by poor alignment and improper installation during the installation process.

4) The center line of the linkage part coincides in the cold state, but after a period of operation, due to the deformation of the rotor fulcrum and foundation, the center line is destroyed again, and vibration occurs.

5) The gears and couplings connected to the motor are faulty, the gears are badly engaged, the gear teeth are worn out, the lubrication of the gears is poor, the coupling is skewed, misaligned, the gear coupling is not correct in tooth profile, tooth pitch, and excessive clearance. Large or severe wear will cause a certain amount of vibration.

6) Defects in the structure of the motor itself, elliptical journal, bent shaft, too large or too small gap between shaft and bearing bush, insufficient rigidity of the bearing seat, foundation plate, certain part of the foundation and even the entire motor installation foundation.

7) Installation problems, the motor and the base plate are not firmly fixed, the foot bolts are loose, and the bearing seat and the base plate are loose.

8) Excessive or too small clearance between the shaft and the bearing bush can not only cause vibration, but also cause abnormal lubrication and temperature of the bearing bush.

9) The load driven by the motor conducts vibration, such as the vibration of the fan and water pump driven by the motor, which causes the motor to vibrate.

10) AC motor stator wiring error, wound asynchronous motor rotor winding short circuit, synchronous motor excitation winding short circuit, synchronous motor excitation coil connection error, cage asynchronous motor rotor broken, rotor core deformation caused the stator and rotor air gap Even, resulting in an imbalance of the air gap magnetic flux and causing vibration.

The harm of motor vibration

The vibration of the motor will shorten the winding insulation and bearing life, and affect the normal lubrication of the sliding bearing. The vibration force promotes the expansion of the insulation gap, causing external dust and moisture to invade it, resulting in a decrease in insulation resistance and an increase in leakage current, and even an insulation breakdown Wait for the accident. In addition, the vibration of the motor will easily cause the water pipe of the cooler to crack and the welding point will vibrate. At the same time, it will cause damage to the load machinery, reduce the accuracy of the workpiece, cause fatigue of all mechanical parts subject to vibration, and loosen the anchor screws. Or if it is broken, the motor will cause abnormal wear of the carbon brushes and slip rings, and even severe brush fire will burn the collector ring insulation, and the motor will produce a lot of noise. This situation usually occurs in DC motors.

Causes of vibration and typical cases

There are three main reasons for vibration: electromagnetic reasons; mechanical reasons; electromechanical hybrid reasons.

1. Electromagnetic reasons

    (1) Power supply: the three-phase voltage is unbalanced, and the three-phase motor runs under phase loss.

    (2) Stator: stator core becomes elliptical, eccentric, and loose; stator winding has broken wire, ground breakdown, inter-turn short circuit, wiring error, and stator three-phase current is unbalanced.

For example:

Red powder was found in the stator core before the boiler room sealing fan motor was overhauled. It is suspected that the stator core is loose, but it is not within the scope of the standard overhaul, so it has not been processed. The motor made a piercing squeal during the test run after the overhaul. Replace it. Troubleshooting after the stator is installed.

    (3) Rotor failure: the rotor core becomes elliptical, eccentric or loose. The rotor cage bar is unwelded with the end ring, the rotor cage bar is broken, the winding is wrong, the brush contact is poor, etc.

For example:

    During the operation of the toothless saw motor in the sleeper section, the stator current of the motor was found to swing back and forth, and the motor vibration gradually increased. According to the phenomenon, it was judged that the motor rotor cage bar might be welded and broken. After the motor was disassembled, it was found that the rotor cage bar was broken in 7 places, which was serious. The two sides and the end ring have all broken. If it is not found in time, it may cause a bad accident of stator burning.

2. Mechanical reasons

(1) Motor itself:

Unbalanced rotor, bent shaft, deformed slip ring, uneven air gap between stator and rotor, inconsistent magnetic center of stator and rotor, bearing failure, poor foundation installation, insufficient mechanical strength, resonance, loose anchor screws, motor fan damage.

Typical Case:

After replacing the upper bearing of the condensate pump motor in the factory, the shaking of the motor increased, and there were slight signs of sweeping in the rotating and stator. After careful inspection, it was found that the motor rotor was not raised at the correct height and the magnetic center of the rotating and stator was not aligned. Re-adjust the thrust head screw After the cap is prepared, the motor vibration fault is eliminated. The vibration of the cross-line hoisting ring hoisting motor has been large after overhaul, and there are signs of gradual increase. When the motor is off the hook, it is found that the vibration of the motor is still large, and there is a large string movement in the axial direction. It is found that the rotor core is loose after disassembly. , The balance of the rotor is also problematic. After replacing the spare rotor, the fault is eliminated, and the original rotor is returned to the factory for repair.

(2) Coordination with the coupling: the coupling is damaged, the coupling is poorly connected, the coupling is not centered correctly, the load is unbalanced, and the system is resonant.

The shaft system of the linkage part is misaligned, the center line does not coincide, and the centering is incorrect. This kind of failure is mainly caused by poor alignment and improper installation during the installation process. There is another situation, that is, the center lines of some linkage parts coincide in the cold state, but after a period of operation, due to the deformation of the rotor fulcrum and foundation, the center line is destroyed again, and vibration occurs.

a. Circulating water pump motor, the vibration has been too large during operation, there is no problem in the motor inspection, and everything is normal without load. The pump team thinks that the motor is running normally, and finally checked that the motor alignment center difference is too large. After the pump team re-aligned , The motor vibration is eliminated.

b. After replacing the pulley in the boiler room induced draft fan, the motor vibrates during trial operation and the three-phase current of the motor increases. Check all circuits and electrical components without problems. Finally, the pulley is found to be unqualified. After the replacement, the vibration of the motor is eliminated, and the three-phase motor is at the same time The current also returned to normal.

3. Reasons for motor mixing

(1) Motor vibration is often caused by uneven air gap, which causes unilateral electromagnetic tension, and unilateral electromagnetic tension further increases the air gap. This electromechanical hybrid effect is manifested as motor vibration.

(2) The motor axially moves in series. The electromagnetic tension caused by the gravity or installation level of the rotor itself and the wrong magnetic center will cause the motor to move in the axial direction and cause the motor to vibrate. In severe cases, the shaft wears the roots, which makes the bearing bushes. The temperature rises rapidly.

(3) The gears and couplings connected to the motor are faulty. This kind of failure is mainly manifested as poor gear engagement, serious gear tooth wear, poor lubrication of the wheel, coupling skew, misalignment, gear coupling tooth profile, incorrect tooth pitch, excessive clearance or serious wear, which will cause certain problems. vibration.

(4) Defects of the motor's own structure and installation problems. This kind of failure is mainly manifested as the ellipse of the shaft journal, the bending of the rotating shaft, the excessive or small gap between the shaft and the bearing bush, the insufficient rigidity of the bearing seat, the foundation plate, the foundation and the entire motor installation foundation, and the motor and the foundation plate are fixed. Insufficient, loose foot bolts, looseness between the bearing seat and the base plate, etc. The gap between the shaft and the bearing bush is too large or too small can not only cause vibration, but also cause abnormal lubrication and temperature of the bearing bush.

(5) The load driven by the motor conducts vibration. For example: the vibration of the steam turbine of the steam turbine generator, the vibration of the fan and water pump driven by the motor, and the vibration of the motor.

How to find the cause of vibration

To eliminate motor vibration, we must first find out the cause of the vibration. Only when the cause of vibration is found can we take targeted measures to eliminate motor vibration.

1. Before the motor is stopped, use a vibration meter to check the vibration of each part. For the parts with greater vibration, test the vibration value in three directions according to the vertical and horizontal axis. If the anchor screw is loose or the bearing end cover screw is loose, you can Fasten directly. After fastening, measure the vibration level to observe whether it is eliminated or reduced. Secondly, check whether the three-phase voltage of the power supply is balanced and whether the three-phase fuse is blown. The single-phase operation of the motor can not only cause vibration, but also It will also cause the temperature of the motor to rise rapidly. Observe whether the pointer of the ammeter swings back and forth, and the current swing occurs when the rotor is broken. Finally, check whether the three-phase current of the motor is balanced. If the problem is found, contact the operator and stop the motor to avoid burning the motor. damage.

2. If the vibration of the motor is not resolved after the surface phenomenon is processed, continue to disconnect the power supply, untie the coupling, and mechanically separate the load connected to the motor. Single-turn motor. If the motor itself does not vibrate, the source of vibration is indicated. It is caused by the coupling failure or the load machinery. If the motor vibrates, it means that the motor itself has a problem. In addition, the power-off method can be used to distinguish between electrical and mechanical reasons. When the power is cut off, the motor will not vibrate or immediately If the vibration is reduced, it is due to electrical reasons, otherwise it is a mechanical failure.

Repair the cause of the failure

1. Overhaul for electrical reasons:

The first is to determine whether the three-phase DC resistance of the stator is balanced. If it is unbalanced, it means that there is an open welding phenomenon in the welding part of the stator connection. Disconnect the winding and separate the phases for searching. In addition, whether there is a short circuit between the windings. If the fault is obvious, it can be isolated from the insulation. If you see burnt marks on the surface, or measure the stator winding with an instrument, and after confirming the short circuit between the turns, take the motor winding off the wire again.

For example: water pump motor, the motor not only vibrates, but the bearing temperature is too high. The small repair test found that the motor's DC resistance is unqualified, and the motor stator winding has open welding. After the fault is found and eliminated by the troubleshooting method, the motor runs normally.

2. Maintenance for mechanical reasons:

Check whether the air gap is uniform, if the measured value exceeds the standard, readjust the air gap. Check the bearing, measure the bearing clearance, if it is unqualified, replace with a new bearing, check the deformation and looseness of the iron core, the loose iron core can be glued and filled with epoxy resin, check the shaft, repair the curved shaft, re-work or direct the straight shaft , And then do a balance test on the rotor. During the trial operation after the blower motor was overhauled, the motor not only vibrated greatly, but also the bearing bush temperature exceeded the standard. After several days of continuous treatment, the fault remained unresolved. My team members found that the air gap of the motor was very large and the level of the tile seat was unqualified. After finding the cause of the fault, after re-adjusting the gaps of each part, the motor was successfully tested once.

3. The mechanical part of the load is checked normally:

There is no problem with the motor itself. The cause of the fault is caused by the connection part. At this time, check whether the basic horizontal plane, inclination, strength, center alignment of the motor is correct, whether the coupling is damaged, and whether the motor shaft extension winding meets the requirements. Wait.